Officials say a plan to build an annex at a severely overcrowded elementary school in Woodside will be difficult because of space.

PS 11 at 54-25 Skillman Ave. is at 20 percent overcapacity with 220 of its youngest students spilling into more than decade-old temporary portable units. Last spring, the Fire Department issued a citation to the school for teaching students in the hallway.

The SCA announced the annex plan in November, something the District 30 Community Education Council, Principal Anna Efkarpides and area politicians have strived for for about nine years. The construction is slated for completion in 2016.

“We’ve looked all around,” School Construction Authority President Lorraine Grillo said of the organization’s decision to build the annex in the backyard of PS 11 at a meeting at the school on Friday morning. “It will be a difficult construction, but at the end of the day ,we will do it well.”

The 350-seat annex, designed by Omni Associates, will be built in the enclosed area behind the main school where the portable units and a few basketball courts sit.

A smaller school, built in 1990, flanks the space on the 54th Street side. The main facility surrounds the yard from the Roosevelt Avenue and 56th Street entrances. The back of the lot slopes steeply down to Doughboy Park.

The limited area around the buildings and the steep incline will make staging for construction complicated, according to Grillo. The SCA will try not to displace outdoor play space, she added.

These challenges prompted the portable units to be installed by crains, Community Education Co-Chairman Jeff Guyton said.

The annex will add about 100 children to the group of 1,350 students already attending PS 11. “This will make this a very large school,” Grillo said. But along with the challenges, the project boasts some positives.

The not-so-temporary, leaky, portables will be replaced.

“Our kids should never be forced to learn in trailers that are falling apart. They deserve the newest and the best school facilities,” said Councilman Jimmy Van Bramer (D-Sunnyside).

The SCA will work with the school to decide where students should be taught during construction. Guyton has said in the past, the not-yet-completed PS 339, one block away at at 39th Avenue and 57th Street, could act as a swing school.

Another positive is that the annex will connect to the school’s main building. Students will not need to go out into the sometimes-inclement weather to get to the cafeteria, Efkarpides said.

The construction addresses safety issues as well. The back gate cannot be locked because of the entrance to park, she said. Having all the students in conjoining buildings will make it easier to monitor entrances.

Most of all, the annex adds more space for students.

The annex is one of five school buildings being built in Long Island City, Woodside and Sunnyside. The combination of these schools will add over 2,000 seats to the 26th Council District.